In modern commercial mobile communication networks, such as, for example WCDMA HSPA (Wideband Carrier Division Multiple Access High-Speed Packet Access)-networks, theoretic bit rates of up to 14 Mbit/s in DL (Downlink) and up to 5.7 Mbps when using the enhanced WCDMA UL (Wideband Carrier Division Multiple Access Uplink, also called EUL) are possible. These high bit rates are achieved by adaptive modulation and coding schemes, fast link adaptation and transmission resource scheduling.
One problem when trying to achieve efficient utilization of the available resources on a radio channel and at the same time providing sufficient user satisfaction (which is related to throughput and delay) is the signaling overhead. Signaling overhead increases the interference in a cell and decreases the actual capacity.
The transmission of data over the air, is performed by using several different physical channels per user equipment (UE). For example, using EUL (UE to base station transmission) the channels DPCCH, E-DPCCH and E-DPDCH are used. UL DPCCH (Uplink Dedicated Physical Control Channel) contains the pilot bits and the power control bits, necessary for making a efficient decoding of the data. The data is transmitted in the E-DPDCH (Enhanced Dedicated Physical Data Channel). When data is transmitted the E DPCCH (Enhanced Dedicated Physical Control Channel) is also necessary, which contains information about the actual packet size and scheduling information etc. In previous standard of the WCDMA, each user using EUL must always transmit the DPCCH, even though no actual data is transmitted. When data is to be transmitted, E-DPDCH and E-DPCCH are used during the transmission period. The power of the E-DPDCH and E-DPCCH are set according to a power offsets compared to the power of the DPCCH.
Since the UL DPCCH is continuously transmitted it causes a major part of the overhead and increases the interference.
Moreover, the DPCCH transmission consumes valuable battery power from the mobile terminal.
One known solution to the control signaling overhead is the principle of “gating”, meaning that DPCCH is not sent continuously, but rather in either well defined time periods on a dedicated control channel or when data is sent on the uplink. Gating may be used also with so called preambles, meaning that the next transmission of DPCCH is done prior to transmitting data on a separate physical channel. These preambles may be one or more time slots long (one time slot is 0.667 ms in WCDMA). WCDMA 3GPP Rel-7 (Third Generation Partnership Project Release 7) includes a gating concept for WCDMA EUL (called UE DTX in the standard).
Some different variants of gating with preambles and different gating intervals are shown in FIG. 1. For example, in 130 the interval of the gating update is 6 slots, and the length of gating update burst is 3 slots and the preamble (preceding actual data E-DPDCH transmission) length is also 3 slots (same as 120).
There are several patents in this area, for example US2007/0030828 and US2007/0030829. However, in some situations, even gating will not perform very well and may lead to lower user satisfaction than no gating. The above mention patents do not address this issue. Examples of such situations may be when mobile terminals move at high speed, such as around 25 m/s or faster. Fast fading in this case will lead to rapidly changing channel conditions and render CQI reports inaccurate. Also, simulations in the high-speed case have shown that the relatively slow power control signaling due to gating will in fact degrade system performance compared to no gating.
The present invention aims at addressing at least some of the problems related to known technology.